1. Field of the Invention
The subject invention generally relates to electromechanical control devices of the type used to provide electrical signals in response to operator-executed manipulations or inputs. In addition, the invention relates to control devices such as disclosed in co-pending U.S. Pat. application Ser. No. 914,527, an Ultrasonic Control Device, filed on June 12, 1978, on an invention by Robert J. Salem, the application having been assigned to the assignee herein, the General Electric Company.
2. Description of Prior Art
Prior art considered relevant to the invention disclosed hereinbelow is described in U.S. Pat. No. 3,834,233, which relates to apparatus for monitoring the surface level of liquid in a container. The apparatus disclosed includes an ultrasonic waveguide vertically extending into the container, the lower end of the waveguide being located so as to be below the lowest liquid surface expected to be measured. Vents in the waveguide cause the liquid surface within the waveguide to settle at the same level as the liquid surface in the container and, as described below, is monitored to provide the information desired. The waveguide supports at its upper end a transceiver which periodically generates pulses of ultrasonic vibrations, and, at a fixed distance below the upper end, an ultrasonic transducer, In operation, the ultrasonic pulses propagate down the waveguide and, as any given pulse moves down the waveguide, it strikes the transducer and continues towards the liquid surface where it is reflected back to the transceiver. The period of time between transmitted pulses is sufficient to allow the return of a reflected pulse to the transceiver before the next of the periodic pulses is transmitted. In response to incident pulses the transceiver and transducer provide electrical signals which are processed to provide a transit time ratio and, since the distance from the transceiver to the transducer is fixed, a periodic measure of the distance from the transceiver to the surface of the liquid in the container. Transit time ratios are processed by the apparatus so as to make the distance measurement independent of the speed of propagation of the pulses, which speed is sensitive to the temperature of whatever gas is located above the liquid level in the waveguide. The patent also discloses that the transducer can be replaced by a reflector and that reflected signals, from the reflector and liquid surface, incident on the transceiver can be similarly processed to provide a measure of distance to the liquid surface in the waveguide.
Persons involved in producing consumer products of the type wherein operation of the product requires one or more operator inputs are aware that potentiometer circuits, electrical switches and electrical switch arrays can be used to control product functions. These persons are also aware that these control devices are expensive to buy, make, or use and contribute substantially to the costs of manufacturing the products.